Battery packs are commonly used for supplying power in electric vehicles. With a development of new energy industry, electric vehicles have become popular. An electric vehicle can catch fire when there is an abnormal electrical connection in a battery pack in the electric vehicle. Thus it is important to detect connection status of connecting wires in a battery pack to avoid inflammation of an electric vehicle, or any device including the battery pack. However, because connecting wires are inside the battery pack which is usually installed inside an electric vehicle, it is not convenient for a user to open the battery pack to directly check the connection status of connecting wires. Therefore, there exists a need of a method for detecting abnormality of a battery pack without opening the battery pack.